The instant invention relates to a process for the continuous production of a lower aliphatic alcohol, such as isopropanol and sec. butyl alcohol, by the direct hydration of the corresponding olefins, namely propene and n-butene, in the presence of a strongly acidic cation exchange resin catalyst in a single-tube reactor with discretionary diameter as fixed bed sump reactor.
In DE-AS No. 24 29 770 (second publication) a process for the continuous production of lower alcohols in the presence of strongly acidic cation exchange resins was disclosed. The alcohol obtained was removed overhead as vapor together with excess reaction gas. After separating the gas, 80% alcohol was obtained. However, in this process, the reaction water and reaction gas were separately preheated and evaporated. Since the reactor bed cools noticeably as the reaction proceeds and this after a traverse of only 0.8 to 1.2 meters in the reaction tube, the maximum practical tube diameter for this process is only about 100 mm. Therefore, the commercial reactors used for this process have been multitube reactors. When a sump operation is employed in these reactors, the uniform distribution of the gaseous and liquid phases presents difficulties.
The cooling effect observed during the course of the reaction was not understood. It is known from DA-AS No. 14 93 190 that gases under supercritical conditions absorb alcohols which can be recovered by pressure release or by heating at a constant pressure. On page 9, lines 10 through 23 and 53 through 67 of the last mentioned patent application, it is stated that the absorption and recovery of such alcohols or other materials does not cause noticeable cooling or heating effects in the system.
It has now been found that under supercritical conditions the propene/propane and n-butene/n-butane reaction gas mixtures, particularly under reaction conditions of 135.degree. C. to 145.degree. C. and min. 60 bar, and 155.degree. to 165.degree. C. and min. 40 bar, respectively, absorb 1.4 % wt. and 1.8 % wt. water, respectively, irrespective of the loading of gases with alcohol. Owing to the absorption of these amounts of water and also of the alcohol in the catalyst bed, the temperature in reactors having a large diameter, e.g. a diameter greater than 150 mm drops substantially after a short distance or passage of the reactants in the reactor even when the tube is externally heated. This occurs despite the heat of formation produced in the reaction of 37.6 KJ/mole for SBA and 50.2 KJ/mole for IPA with the result that the reaction nearly causes.
A method has been found which prevents the harmful cooling of the reactor bed in the above-described process.
The object of the present invention is to provide an improved process for the production of a lower aliphatic alcohol by the direct hydration of the corresponding aliphatic olefin in a large diameter single-tube sump reactor which facilitates the maintenance of a constant temperature and pressure in the reactor.